Technical Field
Embodiments of the subject matter disclosed herein generally relate to the field of geophysical data acquisition and aggregation. In particular, the embodiments disclosed herein relate to a modular autonomous geophysical data recording device and a method and system for managing such devices during a geophysical survey.
Discussion of the Background
Geophysical data is useful for a variety of applications such as weather and climate forecasting, environmental monitoring, agriculture, mining, and seismology. As the economic benefits of such data have been proven, and additional applications for geophysical data have been discovered and developed, the demand for localized, high-resolution, and cost-effective geophysical data has greatly increased. This trend is expected to continue.
For example, seismic data acquisition and processing may be used to generate a profile (image) of the geophysical structure under the ground (either on land or seabed). While this profile does not provide an exact location for oil and gas reservoirs, it suggests, to those trained in the field, the presence or absence of such reservoirs. Thus, providing a high-resolution image of the subsurface of the earth is important, for example, to those who need to determine where oil and gas reservoirs are located.
Traditionally, a land seismic survey system 10 capable of providing a high-resolution image of the subsurface of the earth is generally configured as illustrated in FIG. 1a (although many other configurations are used). System 10 includes plural receivers 12 and acquisition units 12a positioned over an area 13 of a subsurface to be explored and in contact with the surface 14 of the ground. A number of vibroseismic or other types of sources 16 are also placed on surface 14 in an area 17, in a vicinity of area 13 of receivers 12. A recording device 18 is connected to a plurality of receivers 12 and placed, for example, in a station-truck 20. Each source 16 may be composed of a variable number of vibrators or explosive devices, typically between 1 and 5, and may include a local controller 22. A central controller 24 may be present to coordinate the shooting times of the sources 16. A GPS system 26 may be used to time-correlate sources 16 and receivers 12 and/or acquisition units 12a. 
With this configuration, sources 16 are controlled to generate seismic waves, and the receivers 12 record waves reflected by the subsurface. Typically, the receivers 12 and acquisition units 12a are connected to each other and the recording devices with cables 30.
When surveying larger areas, it is desirable to maintain a certain density of receivers 12 over a given area in order to provide data of sufficient quality to accurately image the subsurface. However, covering such a large area, with the same density of receivers 12 as used in a smaller survey, may not be practical, particularly when the receivers 12 are interconnected with cables. As a result, larger surveys often “roll” a set of cable-free autonomous receiving units (referred to individually as “nodes” and collectively as a “spread”) that are equipped with batteries. In such rolling surveys, recovery of the data from each geophysical sensing node may be time consuming, often requiring the nodes to be brought to staging area for a period of time. In the staging area the batteries are also recharged, or removed and replaced. During this time the node is out of service and so a large “float” of nodes is required to facilitate operations.
While “rolling” the nodes in a survey facilitates surveying a large area with a limited number of nodes, a certain portion of the nodes are relegated to the staging area for servicing often resulting in operational delays and increased costs. Given the foregoing, there is a need of a better method and system for rolling the nodes of an active spread. In response thereto, the inventors have developed a modular autonomous geophysical sensing unit, described in co-pending U.S. patent application Ser. No. 14/048,440, entitled “GEOPHYSICAL DATA ACQUISITION AND POWER TRANSFER METHOD APPARATUS AND SYSTEM”, which is incorporated herein by reference. Furthermore, a method and system that leverage such modular sensing units and simplify the node rolling process are described herein.